Recently, electronic devices are gradually becoming lighter, smaller, thinner and highly integrated in its structure. As a result, many problems attributable to a heat load have been caused due to the increase in heat generation amount per unit volume. Representative problems include, for example, problems directly affecting the performance of an electronic device, such as a decrease in operation speed of a semiconductor due to a heat load of an electronic device, a shortening of lifespan of a battery due to battery deterioration, and the like.
For this reason, the effective heat dissipation in an electronic device is becoming one of very important tasks.
As a heat dissipation means used in an electronic device, graphite having a superior thermal conductivity draws attention. Among them, an artificial graphite sheet which can be easily processed into a sheet form and has a thermal conductivity of about 2 to 7 times higher than the thermal conductivity of copper or aluminum is in the spotlight.
Such an artificial graphite sheet can be obtained through a carbonization process and a graphitization process of a polymer. Among the polymers, a heat-resistant polymer capable of withstanding a temperature of about 400 degrees C. or higher can be used as a graphite precursor. A representative example of such a heat-resistant polymer is polyimide (PI).
Polyimide, which is based on a rigid aromatic main chain and an imide ring having an excellent chemical stability, is a polymer material having the highest level of heat resistance, chemical resistance, electrical insulation and weather resistance among organic materials. Polyimide is known as an optimal graphite precursor because polyimide makes it possible to achieve excellent yield, crystallinity and thermal conductivity in the preparation of an artificial graphite sheet.
In general, the physical properties of an artificial graphite sheet are known to be greatly affected by the physical properties of polyimide as a graphite precursor. Thus, the modification of polyimide has been actively studied in order to improve the physical properties of the artificial graphite sheet. In particular, extensive research is underway to improve the thermal conductivity of the artificial graphite sheet.
Nevertheless, there is no clear result in the development of an artificial graphite sheet having a very high thermal conductivity capable of remarkably improving the performance of an electronic device due to heat dissipation and a polyimide capable of realizing the artificial graphite sheet.
Therefore, it is necessary to develop an artificial graphite sheet having a desired thermal conductivity and a polyimide capable of realizing the artificial graphite sheet.